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Crankcase Pressure #1511856
10/03/13 12:41 PM
10/03/13 12:41 PM
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Sac, CA
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mopowers Offline OP
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I'm in the process of doing some final tuning on my 340. While fiddling with the timing yesterday I noticed a hissing sound after I shut the car off. It's coming from the oil fill cap. The 340 has a PCV on the pass. rear side. Should there be a breather on the opposite side? Should I be concerned about this hissing?



Last edited by mopowers; 10/03/13 01:03 PM.
Re: Crankcase Pressure [Re: mopowers] #1511857
10/03/13 12:57 PM
10/03/13 12:57 PM
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There should be a breather opposite the PCV - regardless of the side it's on. But - what you're hearing is not crankcase pressure as one might think (bad stuff). It's escaping pressure from a cylinder that was sealed when you shut it down. No big deal.


Well, art is art, isn't it? Still, on the other hand, water is water! And east is east and west is west and if you take cranberries and stew them like applesauce they taste much more like prunes than rhubarb does. Now, uh... Now you tell me what you know.
Re: Crankcase Pressure [Re: moper] #1511858
10/03/13 01:17 PM
10/03/13 01:17 PM
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Quote:

There should be a breather opposite the PCV - regardless of the side it's on. But - what you're hearing is not crankcase pressure as one might think (bad stuff). It's escaping pressure from a cylinder that was sealed when you shut it down. No big deal.




The hissing stops as soon as I crack the filler cap. I definitely need a breather there.

So is the pressure just slipping passed the rings of whatever piston moves up on the compression stroke after the engine is shut down?

Re: Crankcase Pressure [Re: mopowers] #1511859
10/03/13 01:29 PM
10/03/13 01:29 PM
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Yes a breather of sorts is needed on both sides. If nothing else, it keeps the gaskets from leaking when crankcase pressure is evident. And yes it's crankcase pressure you're hearing, and probably not cylinder pressure. Especially when it stops as soon as you remove the oil cap.

Re: Crankcase Pressure [Re: mopowers] #1511860
10/03/13 04:49 PM
10/03/13 04:49 PM
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Bend,OR USA
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Quote:

Quote:

There should be a breather opposite the PCV - regardless of the side it's on. But - what you're hearing is not crankcase pressure as one might think (bad stuff). It's escaping pressure from a cylinder that was sealed when you shut it down. No big deal.




The hissing stops as soon as I crack the filler cap. I definitely need a breather there.

So is the pressure just slipping passed the rings of whatever piston moves up on the compression stroke after the engine is shut down?


What your hearing is the motor sucking air into the crankcase, not pressure escaping Try starting the motor up with the oil filler cap off and put your hand(palm) over the hole in the valve cover to see if it has pressure trying to push your hand off or if it ends up making a vacume after running for several minutes The PCV will take several minutes to suck all the air out of the crankcase before it will start making a vacume inside it If it has pressure from blowby it will make pressure as soon as you start it up All motors that use a PCV need a inlet vent, it is best on a V6 or V8 to put it on the other side of the motor away from the PCV as far as possible


Mr.Cab Racing and winning with Mopars since 1964. (Old F--t, Huh)
Re: Crankcase Pressure [Re: mopowers] #1511861
10/03/13 05:49 PM
10/03/13 05:49 PM
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Quote:

The 340 has a PCV on the pass. rear side. Should there be a breather on the opposite side? Should I be concerned about this hissing?



(1) yes in the boss there on the DR front. (2) no. Need a PCV on one side & a breather (open or closed) on the other side


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Re: Crankcase Pressure [Re: RapidRobert] #1511862
10/03/13 07:06 PM
10/03/13 07:06 PM
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Here's a pic of a PCV system. Is there anything in the archives? Maybe there should be? this topic comes up quite often

7875105-Picture1.jpg (53 downloads)
Re: Crankcase Pressure [Re: Dcuda69] #1511863
10/11/13 01:04 PM
10/11/13 01:04 PM
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Sac, CA
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Thanks for the input guys. Can you guys recommend a breather that'll look decent with the valve covers I have?

Also, can I get away with replacing the rear oil fill cap on the driver's side with a breather, or does it need to be in the front boss (opposite corner from the PCV)??

Re: Crankcase Pressure [Re: mopowers] #1511864
10/11/13 07:25 PM
10/11/13 07:25 PM
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It doesn't really matter where you put the inlet side(front or back0 or which side gets the PCV and which side gets the breather All the early(pre 1970) BB had the PVC on the passenger side rear valve cover, the SB had the PVC in the center of the valve covers. Staring in 1970 Mopar made the BB have two different valve covers and moved the PVC to the drivers side rear with the push in breather cap on the passenger side


Mr.Cab Racing and winning with Mopars since 1964. (Old F--t, Huh)
Re: Crankcase Pressure [Re: Cab_Burge] #1511865
10/11/13 11:47 PM
10/11/13 11:47 PM
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Thanks Cab. I'll just stick one in the back and call it good. Have a good weekend.







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